The present invention relates to a multi-layered packaging material for use in wrapping, packaging and shipping articles, and also to a method of forming the multi-layered packaging material.
Packaging materials, used for pre-formed bags and other containers, especially those used for microwave popcorn, have produced new and unforeseen problems as the result of the need to use specific types of packaging materials. Pre-formed microwave popcorn bags typically use packaging materials that include two plys of specially treated paper, with a metallized film or patch interposed therebetween. Because heat assisted metallized films or patches are used in such packaging materials, the paper plys are typically flourocarbon treated paper plys, in order to keep the metallized film or patch from contact with food, while serving as an insulator between the hot surface of the metallized film or patch and the food. In addition, the paper flourocarbon plys are treated also for grease stain resistance, quite obviously to prevent food grease from being transferred through the paper plys.
At the present time, there are two basic types of metallized film strips used for heat assist purposes in microwave packages. One type is a strip of metallized polyester film which has been de-metallized to allow the remaining metallized areas to be in the exact position required to achieve heating of food in the package. The second type is a patch of a metallized film which is die cut and placed in the package by a special machine attachment incorporated in the forming or laminating line.
The new and unforeseen problems that have been encountered, as the result of using packaging materials as described above, relate to the type and amount of adhesive used to laminate the paper plys and metallized film ply or patch to each other, to form the multi-layered packaging material. Adhesives used to laminate the aforementioned plys to one another are FDA approved, water based adhesives that are readily usable in forming or laminating lines.
Unfortunately, these water based adhesives "trap-in" the moisture between the various plys in the packaging material, and this causes slow absorption into the paper plys, with moisture retention even occurring after the food is in a pre-formed bag. The problem is made worse by the use of flourocarbon and grease stain treated papers. As will be appreciated, such papers do not readily permit any wicking action because they are treated to do just the opposite, i.e., to eliminate greasy food stains on the outside of the pre-formed bags. The result is that the paper plys greatly reduce the normal drying action of the water based adhesives and moisture which are trapped inside of the package, making it difficult for rapid wicking of the paper plys. Where moisture from the water based adhesives is trapped inside the paper plys, the pre-formed bag becomes "wet" making it difficult to process, and in some cases, making the food appear less than desirable to eat.
In addition, odor from the adhesive remains within the package due to the lack of drying of the adhesive moisture. All adhesives have odors, even though the adhesive industry has greatly reduced the offensiveness of adhesive odors. Yet, it is still impossible to make an odor free adhesive.
Drying ovens and other equipment can be utilized to assist in the drying process, but this slows the production process, and further the ovens are not completely effective in removing "trapped-in" moisture. The relative large amounts of adhesive that are used also have the potential of possible food contamination, as the result of high temperatures created by the heat assisted metallized strip or patch. Various manufacturing conditions, storage and distribution time, and weather conditions cause the "trapped-in" moisture problem to exist in varying degrees at different times. However, the problem exists in one form or another, varying only in the level or degree of "wetness".
Over the years, various solutions have been proposed, most of which have helped to some degree, including the use of higher oven heat, lower odor adhesive, etc., but none have completely eliminated the odor or "wetness" problem under all types of production, weather, storage and distribution conditions.